Welding systems are known using a laser beam as the energy source for welding various metallic items together. Such a system includes a downwardly directed laser beam and a horizontal worktable on which the work is supported. In many cases, the desired weld is to be formed along a continuous, elongated line. Relative motion between the laser beam and the work is thus required. Either the laser beam is movably mounted to traverse along the weld line or the worktable is movable to cause the weld line to pass beneath a stationary laser beam.
The assignee of this invention has previously used a laser welding system of this type to join together two superimposed metallic sheets. These sheets when joined together form one fin in a heat exchange unit. The joined sheets provide a fin having a central array of corrugated, cooling passages through which a fluid may be passed in a heat exchange relationship with a medium flowing along the outside of the fin. A particular heat exchange unit normally includes a large number of these fins spaced slightly apart so that the heat exchange medium will flow down along both sides of each fin. Heat exchangers of this type are often submersed in water, such as sea water, for cooling heated fluids, such as power plant fluids, that are passed through the cooling passages in the fins.
In making each fin for such a heat exchange unit, a continuous elongated weld is required to join together the two separate metallic sheets that form the fin. This weld line encircles the central array of corrugated cooling passages to prevent any leakage of the fluids contained in those passages. This weld has been formed by the assignee of this invention by moving the laser source relative to the worktable along the weld line in a continuous fashion from one end of the weld line to the other.
One problem associated with the prior known laser welding systems, including those used and known by the Applicants in welding fins for heat exchangers, is the need to firmly clamp the two metallic sheets together. This has conventionally been done by a large number of clamps, or one solid top clamp with a large number of bolts, that surround the peripheral edges of the metallic sheets to clamp them tightly along the entire length of the weld line. This is difficult and time consuming to set up and requires many clamps, or bolts, to effect close contact between the metal sheets. The time and labor involved in the clamping operation raises the costs of producing the fins. Moreover, it is not uncommon for the sheets to sometimes be separated by at least a small gap along at least a portion of the weld line, despite the presence of the clamps, leaving a weaker or non-hermetic weld at that point. This is also obviously undesirable.